Rod assembly for nuclear reactors

ABSTRACT

A rod assembly for a fuel bundle of a nuclear reactor may include an upper end piece, lower end piece and a plurality of rod segments attached between the upper and lower end pieces and to each other so as to form an axial length of the rod assembly. The rod assembly may include an adaptor subassembly provided at given connection points for connecting adjacent rod segments or a given rod segment with one of the upper and lower end pieces. The connection points along the axial length of the rod assembly may be located where the rod assembly contacts a spacer in the fuel bundle. One (or more) of the rod segments may include an irradiation target therein for producing a desired isotope when a fuel bundle containing one (or more) rod assemblies is irradiated in a core of the reactor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to nuclear reactors, and moreparticularly to a rod assembly for a nuclear reactor.

2. Description of the Related Art

A continuing problem during operation of a nuclear reactor is theexistence of debris of various sizes. Examples of such debris mayinclude small-sized fasteners, metal clips, welding slag, pieces ofwire, etc. The debris may be generated as a result of the originalconstruction of the reactor core, subsequent reactor operation and/ordue to repairs made during a planned or unplanned maintenance outage.

During the operation of such nuclear reactors, the debris may be carriedby the cooling water (reactor coolant) and may become wedged between orwithin reactor components such as fuel rods of a fuel assembly in aboiling water reactor (BWR) or pressurized water reactor (PWR), or incontrol rod assemblies in a PWR, etc. The repeated interaction betweenthe entrained debris and component(s) can result in fretting damage tothe component(s), such as damage to the fuel rods.

Some of the debris may be caught between the fuel rods and other fuelassembly components. The debris vibrates in the moving coolant andinteracts with the fuel rods, potentially causing what is known asfretting wear of the fuel rod cladding. This fretting may be recognizedas a significant cause of failure of the fuel rod in a BWR or PWR, forexample.

Conventional solutions have included employing the use of debris filtersto filter the debris from the reactor coolant. These are typicallypositioned in the lower tie plate or nozzle of a fuel assembly and soare replaced when the fuel is discharged. Debris filtering devices havealso been introduced into the nuclear plant piping system. However, thedebris filter and/or external filter mechanisms do not completelyobviate the fretting problem in nuclear reactors. Fretting still mayoccur and cause fuel failures, which may release fuel, fission productsor other rod contents into the coolant, potentially leading to thepremature withdrawal from service of the fuel assembly or costlymid-cycle fuel replacement.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention are directed to a rodassembly for a fuel bundle of a nuclear reactor. The rod assembly mayinclude an upper end piece, lower end piece and a plurality of rodsegments attached between the upper and lower end pieces and to eachother so as to form an axial length of the rod assembly. The rodassembly may include an adaptor subassembly provided at given connectionpoints for connecting adjacent rod segments or a given rod segment withone of the upper and lower end pieces. The connection points along theaxial length of the rod assembly may be located where the rod assemblycontacts a spacer in the fuel bundle. One (or more) of the rod segmentsmay include an irradiation target therein for producing a desiredisotope when a fuel bundle containing one (or more) rod assemblies isirradiated in a core of the reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent by describing, indetail, exemplary embodiments thereof with reference to the attacheddrawing, wherein like elements are represented by like referencenumerals, which are given by way of illustration only and thus do notlimit the exemplary embodiments of the present invention.

FIG. 1A illustrates an exemplary fuel bundle of a nuclear reactor.

FIG. 1B illustrates a spacer-to-rod contact area within the fuel bundle,showing where debris might become lodged or entrained within the fuelbundle of FIG. 1A.

FIG. 1C illustrates a spacer that is restrained between the tabs of atabbed water rod and the contact areas within a spacer where debrismight become lodged or entrained within the fuel bundle of FIG. 1A.

FIG. 2A illustrates a rod assembly for a fuel bundle in accordance withan exemplary embodiment of the invention.

FIG. 2B illustrates an exploded view of a portion of FIG. 2A toillustrate the rod assembly in further detail.

FIGS. 3A and 3B are perspective and side-view profiles illustrating themale adaptor subassembly for the rod assembly in accordance with anexemplary embodiment of the invention.

FIGS. 4A and 4B are perspective and side-view profiles illustrating thefemale adaptor subassembly in accordance with an exemplary embodiment ofthe present invention.

FIGS. 5A and 5B are perspective and side-view profiles illustrating anexemplary lower end piece of the rod assembly in accordance with anexemplary embodiment of the invention.

FIGS. 6A-6E are views illustrating an exemplary container assembly withcontents adapted for insertion in a given rod segment of the rodassembly, in accordance with an exemplary embodiment of the invention.

FIG. 7 illustrates a rod assembly for a fuel bundle in accordance withanother exemplary embodiment of the invention.

FIGS. 8A-B are views illustrating an adaptor subassembly for the rodassembly in accordance with another exemplary embodiment of theinvention.

FIGS. 9A-B are views illustrating a a mini-subassembly for the rodassembly in accordance with another exemplary embodiment of theinvention.

FIGS. 10A-B are views illustrating an upper end plug adaptor for the rodassembly in accordance with another exemplary embodiment of the presentinvention.

FIGS. 11A-B are views illustrating an lower end plug adaptor for the rodassembly in accordance with another exemplary embodiment of the presentinvention.

FIGS. 12A-C are views illustrating an adaptor subassembly for the rodassembly in accordance with another exemplary embodiment of theinvention.

FIG. 13 illustrates the multi-segmented fuel rod 100 of FIG. 2A infurther detail.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1A illustrates an exemplary fuel bundle of a nuclear reactor suchas a BWR. Fuel bundle 10 may include an outer channel 12 surrounding anupper tie plate 14 and a lower tie plate 16. A plurality of full lengthfuel rods 18 and/or part length fuel rods 19 may be arranged in a matrixwithin the fuel bundle 10 and pass through a plurality of spacers (alsoknown as spacer grids) 20 vertically spaced one from the othermaintaining the rods 18, 19 in the given matrix thereof.

The fuel rods 18 and 19 with at least a pair of water rods 22 and 24 maybe maintained in spaced relation to each other in the fuel bundle 10 bya plurality of spacers 20 provided at different axial locations in thefuel bundle 10 so as to define passages for reactor coolant flow betweenfuel rods 18, 19 in the fuel bundle 10. There may typically be betweenfive to eight spacers 20 spaced along the entire axial length of thefuel bundle 10 for maintaining the fuel rods 18, 19 in the desired arraythereof. Spacer 20 may be embodied as any type of spacer, for example,ferrule-type spacers or spacers of the type described and illustrated inU.S. Pat. No. 5,209,899.

In FIG. 1A, the matrix may be a 10×10 array, although the illustrativefuel bundle 10 may have a different matrix array of rods 18, 19 such asa 9×9 array. The bundle 10 may include all full length fuel rods 18and/or a combination of full 18 and part length 19 fuel rods, as isknown. Each of the full length fuel rods 18 and part length fuel rods 19is cladded, as is known in the art. The water rods 22 and 24 (two areshown, there may be more or less water rods in bundle 10) may bedispersed among the fuel rods 18, 19 in bundle 10, between the lower tieplate 16 and the upper tie plate 14. The water rods 22, 24 serve totransfer fluid from the lower regions of the nuclear fuel bundle 10 tothe upper regions, where the water is dispersed through openings locatedat the top of the water rods, as shown.

FIG. 1B illustrates a spacer to rod location in the fuel bundle 10 ofFIG. 1A. In particular, FIG. 1B illustrates exemplary debris catchingareas 50 a-50 d between a given fuel rod 18 and spacer 20 to show wheredebris might be caught or entrained so as to exacerbate the frettingproblem.

FIG. 1C illustrates a spacer to water rod location in the fuel bundle 10of FIG. 1A and exemplary debris catching areas 50 a-50 e between a givenwater rod 22, 24 and spacer 20 to show where debris might become lodgedor entrained so as to potentially causing fretting with an adjacent rod18, 19. The water rods 22 and 24 are bound by a spacer 20. Spacer 20 isbound by a pair of radial directed flanges or tabs 34 and 36 which lieon opposite sides of the spacer 20, to maintain the spacer at thedesired elevation. During reactor power operations, debris may becarried by the reactor coolant and may become lodged in and around thecircumference of the water rods 22, 24 and spacer 20 within bundle 10.The repeated interaction between the entrained debris at spacer 20 andthe water rods 22, 24 can result in the aforementioned fretting wear andpotential damage to the adjacent rods 18, 19 and/or the water rods 22,24.

FIG. 2A illustrates a rod assembly 100 for a fuel bundle 10 inaccordance with an exemplary embodiment of the invention. In an effortto provide a fretless rod designed so as to substantially eliminatefretting wear as described in a conventional art, there is described arod assembly 100 (also occasionally referred to as a multi-segment rodor multi-part rod) that includes a plurality of parts or cladded rodsegments 110. As shown in FIG. 2A, a rod assembly 100 may include aplurality of rod segment 110 (two adjacent rod segments shown as 110 aand 110 b) between an uppper end piece 120 and a lower end piece 130.The upper end piece 120 and lower end piece 130 may include threads tomate with the lower and upper tie plates of the fuel bundle 10 (notshown), as is known. Adjacent rod segments 110 a, 110 b may beinterconnected to each other via at least one adaptor subassembly, showngenerally as a subassembly 300 within the dotted line circle of FIG. 2A.Only one rod assembly 100 is shown in FIG. 2A, it being understood thatone or more of the rod assemblies 100 shown in FIG. 2A may be insertedinto a fuel bundle such as the bundle 10 shown in FIG. 1A.

Rod segments 110 may be attached between the upper and lower end pieces120, 130 and to each other so as to form the entire axial length of therod assembly 100. In an example, a rod segment 110 a, a rod segment 110b and one each of the upper and lower end pieces 120, 130 may beconnected by adaptor subassemblies 300 at connections points along theaxial length of the rod assembly 100 where the rod assembly contactsspacers 20. Although only three spacers 20 and adaptor subassemblies 300are shown in FIG. 2A for reasons of brevity, it should be understoodthat the fuel bundle 10 could include one or more rod assemblies 100,each having at least one rod segment 110 a and at least one rod segment110 b connected by adaptor subassemblies 300 at any number of spacer 20locations. The rod segments 110 a, 110 b may be fixed length segments tofacilitate the manufacturing process. Similarly, the adaptorsubassemblies 300 may also be manufactured at a fixed size so as to beof equal lengths.

In this exemplary embodiment, the rod segments and adaptor subassembliesare constructed of a material which is corrosion resistant andcompatible with the other reactor components. An exemplary material maybe a zirconium alloy, for example.

Desirably, a portion of each spacer 20 contacts the rod assembly 100 ateach of the adaptor subassemblies 300 so as to substantially coveradaptor subassemblies 300 and/or connection points 115 between rodsegments 110, or substantially covers an adaptor subassembly 300 orconnection point 115 connecting a given rod segment 110 and one of theupper and lower end pieces 120 and 130. Accordingly, the consequences offretting of the rod assembly 100 at these points 115 and/or adaptorsubassemblies 300 within a given spacer 20 may be eliminated. Whilefretting may still occur, the fretting wear on the rod assembly 100occurs on the adaptor subassembly 300, instead of on a segment 110 a, b.Accordingly, this may eliminate to potential release of contents fromwithin a given rod segment 110 to the reactor coolant.

FIG. 2A illustrates an exemplary adaptor subassembly 300 betweenadjacent rod segments 110 a and 100 b in transparent detail (i.e.,phantom lines illustrate components within rod segments 110 and/oradaptor subassemblies 300) so as to show weld points 155 between anadjacent rod segment 110 b and a part of the adaptor subassembly 300.FIG. 2A also illustrates (in phantom) an optional container assembly 600provided within one or more of the rod segments 110 for applicationsdescribed in detail hereafter. The rod segments may or may not include acontainer assembly 600 therein. Additionally, in FIG. 2A, there isillustrated an undercut portion or recessed break line 360. As will bedescribed in further detail below, the recessed break line 360 providesan alternative location to break a particular adaptor subassembly300/rod segment 110 in order to remove a particular rod segment 110 fromthe rod assembly 100, which may be desirable to reduce length intransport, etc., for example.

As shown in FIG. 13, which illustrates the multi-segmented fuel rod 100of FIG. 2A. The multi-segmented fuel rod 100 is broken up into varioussegments 110A, 110B, 110C, 110D, 110E, 110F and 110G that connect toeach other via a corresponding adaptor subassembly 300 at connectionpoints 115 (as previously shown) to form a contiguous multi-segmentedfuel rod 100′ (as evident by the dotted connection lines 111 in FIG.13). FIG. 13 also illustrates enlargements of cross-sectional viewsI-VII of the target container 600 in each of segments 110A, 110C, 110E,110F and 110G of the multi-segmented rod 100.

Views I and II show a plurality of containment structures 600 within rod100 that are housing multiple different targets, shown as a liquid,solid and a gas target 620 within a single rod segment 110A. Further,enlargements I and II illustrate indicia 650 that can be placed on thecontainment structures 600 within a given rod segment 110A, 110C, 110E,etc. As shown, the indicia 650 can indicate whether or not the target isin solid, liquid or gas form, and can also provide the name of thetarget isotope and/or the name of the isotope to be produced due toirradiation, for example (not shown in FIG. 13 for purposes of clarity).

Rod segments 110B and 110D are shown to contain nuclear fuel 660, asshown in enlargements III and IV, for example. Of course in analternative, multi-segmented rod 100 can be composed of a plurality ofrod segments 110 in which no segment 110 includes nuclear fuel, aspreviously described. Enlargement V of rod segment 110 e illustrates acontainer assembly 600 which includes a target that is in gaseous form.Enlargement VI of rod segment 110F illustrates a container assembly 600within the rod segment 110 f that includes a target 620 in liquid form.Enlargement VII of rod segment 110G illustrates a container assembly 600which includes a solid target 620, shown as a single column of Co-59BBs, which can be irradiated to produce the desire isotope, in thiscase, Co-60. Each of the container assemblies 600 can thus beprepackaged with the target 620 isotope material in solid, liquid or gasform, for insertion into a corresponding rod segment 110 of themulti-segmented rod 100, for example.

Further, since each of the container assemblies 600 are sealed by endplugs 630 at one end 612 and by exterior threads 601 and an O-ring 602at the first end 611 (as previously shown in FIGS. 6A, 6D and 6E), theremoval of a particular segment 110 at its connection point 115 (i.e.,at the disconnection of the adapter subassembly 300 at connection point115 between two segments 110) will not cause a breach which would exposethe irradiation target 620 to the reactor coolant. Thus, the containerassembly 600′ together with the outer cladding of the rod segment 110provides a double-walled containment for the irradiation target 620.

FIG. 2B illustrates an exploded view of a portion of FIG. 2A toillustrate the rod assembly in further detail. Portions of FIG. 2B arealso shown in phantom (dotted lines) to indicate components within aninterior of a rod segment 110 a, 110 b or subassembly 300. The adaptorsubassembly 300 may include a male adaptor plug 330 that is attached toa rod segment 110 a via a weld at weld joint 155. Similarly, the adaptorsubassembly 300 may include a female adaptor plug 350 which may beattached at one end to a rod segment 110 b via a weld at weld joint 155.Both the male and female adaptor plugs 330, 350 may include a pluralityof nut-shaped depressions 357 around an outer circumference thereof. Ingeneral, the depressions 357 may facilitate removal/disassembly of agiven rod segment 110, upper end piece 120 or lower end piece 130 by asuitable tool during a maintenance outage, for example.

In FIG. 2B, the depressions 357 may include recessed angled surfaces atopposite ends thereof, such as angle edges 380, to prevent damage to thespacer 20 during insertion or assembly of the rod assembly 100 into thefuel bundle 10 of the reactor. Further, as shown in dotted line form,each of the male and female adaptor plugs 330 and 350 may include weldalignment members 355 to facilitate inserting the corresponding adaptorplug 330, 350 into an end of a given rod segment 110 for welding theplug 330/350 to the segment 110 at the weld joint 155.

FIGS. 3A and 3B are perspective and side-view profiles illustrating partof an adaptor subassembly for the rod assembly in accordance with anexemplary embodiment of the invention. As shown in FIGS. 3A and 3B, maleadaptor plug 330 may be attached (such as by a weld) to rod segment 110at a first end 332. A second end 334 of male adaptor plug 330 may beinserted into a corresponding chamber or cavity of the female adaptorplug 350. The male adaptor plug 330 may include the aforementioned weldalignment member 335 as part of a cylindrical section 333, whichincludes the depressions 357 around the circumference thereof withangled edges 380. An intermediate member 339 connects the cylindricalsection 333 to an elongate section 338. The elongate section 338 may bethreaded, as shown in FIG. 3A. The elongate section 338 tapers into agenerally cone-shaped end 336 at the male adaptor plug second end 334.The cone-shaped end 336 represents a self-alignment aid for connectingthe female adaptor plug 350 to the male adaptor plug 330 as a singleadaptor subassembly 300.

The male adaptor plug 330 may be made of a material that is corrosionresistant and compatible with the other reactor components, such as azirconium alloy, as is known in the art.

FIGS. 4A and 4B are perspective and side-view profiles illustratinganother part of the adaptor subassembly in accordance with an exemplaryembodiment of the present invention. As shown in FIGS. 4A and 4B, femaleadaptor plug 350 has a first end 352 for attachment to a given rodsegment 110 (not shown) and a second end 354 for receiving thecone-shaped end 336 and elongate member 338 of the male adaptor plug 330therein. Female adaptor plug 350 may include weld alignment member 355and a generally cylindrical section 353, which has a plurality ofnut-shaped 357 depressions around the circumference with angled edges380 at the first end 352 to facilitate removal of the female adaptorplug 350 and/or removal of an adjacent rod segment.

The female adaptor 350 includes an interior cavity 358. A surface of thecavity 358 may include a plurality of mating threads 356 for receivingcorresponding threads (see FIG. 3A) on the elongate section 338 of themale adaptor plug 330. The cavity 358 may have a concave angled portion359 at an end thereof that is configurable as a self-alignment aid forreceiving the cone-shaped end 336 to connect male adaptor plug 330within the female adaptor plug 350.

As shown in FIG. 4B, the cylindrical section 353 of the female adaptorplug 350 may include a recessed break line 360 at second end 354. Therecessed break line 360 may also be referred to as an undercut section,for example. Undercutting may be designed into each of the adaptorsubassemblies 300 so that a given rod segment 110 may be safely brokendown by snapping and/or cutting a section loose without unscrewing theconnecting joints 115 of FIG. 2B. This will be illustrated in furtherdetail below.

In another aspect, as the threads of the elongate section 338 engage thecorresponding mating threads 356 within the cavity 358 of the femaleadaptor plug 350, the recessed break line 360 aligns with theintermediate member 339 of the male adaptor plug 330. Since the diameterof the intermediate member 339 is less than a diameter of thecylindrical section 333, this represents a ‘weakened area’ thatfacilitates cutting, snapping or breaking of the adaptor subassembly 300of FIG. 2B at that location. The recessed break line 360 may thusprovide a visual identification as to where to cut an adaptorsubassembly 330 of FIG. 3B, in the event of segment 110 of FIG. 2Breplacement, adaptor subassembly 300 of FIG. 2B replacement, etc.

FIGS. 5A and 5B are perspective and side-view profiles illustrating anexemplary lower end piece of the rod assembly in accordance with anexemplary embodiment of the invention. As shown in FIGS. 5A or 5B, oneor both of the upper and lower end pieces 120 and 130 of FIG. 2A may beformed as a solid end piece assembly 500. The solid end piece assemblymay be made of a solid metal material for example. End piece assembly500 may include an end plug portion 505 at one end thereof and may havean integral end piece adaptor subassembly 530 at another end thereof forthreaded engagement with a corresponding female adaptor segment 350 ofFIG. 4B within an adjacent rod segment 110 of FIG. 2B.

The end piece assembly 500 may be fabricated of solid Zircaloy and doesnot necessarily have any nuclear fuel (enriched uranium) or poisons(gadolinium) loaded therein, since axial flux near the top and bottom ofa fuel bundle such as fuel bundle 10 of FIG. 1A is generallysubstantially lower than between the upper and lower end pieces 120 and130 of FIG. 2A, for example. FIGS. 5A and 5B thus may illustrate areusable end plug (reusable as either an upper end piece or lower endpiece) that can be removed with relative ease from an adjacent segment110 of FIG. 2B of the rod assembly 100 of FIG. 2A during a scheduledmaintenance outage.

FIGS. 6A-6E are views illustrating an exemplary container assembly withcontents adapted for insertion in a given rod segment 110 of the rodassembly 100 of FIG. 2A, in accordance with an exemplary embodiment ofthe invention.

In an exemplary embodiment of the present invention, various ones of therod segments 110 may include a container assembly 600 therein, as shownpreviously in FIG. 2B. In an example, the container assembly 600 mayhouse or contain selected contents. An example of such contents may beone or more irradiation targets that produce one or more desiredisotopes when a fuel bundle containing the rod assembly 100 isirradiated in the core of the reactor. One or more rod segments 110 ofthe rod assembly 100 may each include the same target, different targetsor multiple irradiation targets, for example.

Referring to FIGS. 2A and 2B, in one exemplary aspect of the invention,at least one of the rod segments 110 of rod assembly 100 includes acontainer assembly 600 therein, and none of the other rod segments 110of rod assembly 100 (nor either of the end pieces 120, 130) contain anynuclear fuel/poisons. In another aspect, one or more of the rod segments110 of rod assembly 100 may include desired enrichments of uraniumand/or concentrations of gadolinia. The locations and concentrations maybe based on the desired characteristics of the bundle 10 for a plannedenergy cycle, for example. A rod segment 110 that includes anirradiation target may not also include nuclear fuel, although adjacentrod segments 110 could include nuclear fuel therein.

Referring now to FIGS. 6A-6E, the container assembly 600 shown initiallyin phantom in FIGS. 2A and 2B may include a container 610 that houses anirradiation target 620 therein. The container 610 may be closed at oneend 611, open at the other end 612 and may include a seal 613 to closethe container by a suitable end cap 630, as shown in FIG. 6D, althoughend caps 630 may be provided at both ends. Although container 610 isshown as having a generally cylindrical shape, container 610 may beoriented in any geometrical shape so long as the largest diameter of theshape is less than the inner diameter of rod segment 110. Container 610may be made of a suitable material such as zirconium alloys, forexample.

Container 610 may house one or more irradiation targets 620. Theirradiation target 620 shown in FIG. 6B is illustrated in a generallycylindrical form or shape. However, the irradiation target 620 may beembodied as a solid, liquid and/or gas, and may take any geometry solong as the diameter of the geometry is small enough to fit inside thecontainer 610 (less than an inner diameter of the container 610) withina given rod segment 110. The container 610, coupled with its cladded rodsegment 110, therefore provides a double-walled containment for theirradiation target 620 when in place within the rod segment 110.

FIG. 6E illustrates a transparent front or side view of containerassembly 600, to show the container 610 housing the irradiation target620 therein and sealed by the end plug 630 at location 613. Optionally,an interior of the container 610 may include a spring 640 to provide acounter force against irradiation target 620 when sealed by end plug630. The end plug 630 may be attached to the container 610 by suitableattachment means, i.e., weld, threaded engagement, friction connection,etc.

In another aspect, the container 600 houses irradiation target 620therein, having a first end 611 that has a pilot hole 603 for removingthe irradiation target 620 after irradiation. The first end 611 mayinclude exterior threads 601 and an O-ring 602 that is used for sealingcontainer 600 when inserted into a piece of equipment. Pilot hole 603has interior threads to aid in the removal of container 600 from the rodsegment 110.

The irradiation target 620 may be a target selected from the group ofisotopes comprising one or more of cadmium, cobalt, iridium, nickel,thallium, thulium isotope, for example, or any other isotope having anatomic number greater than 3. Desirably, a given segment 110 and/orcontainer assembly 600 may include indicia or indicators thereon toindicate what irradiation target 620 is loaded in that rod segment110/container 600, for example, and/or what isotope is to be producedfrom that target. The specific methodology in which one or more of therod assemblies 100 containing irradiation targets is irradiated within afuel bundle (such as fuel bundle 10 of FIG. 1A) of a nuclear reactor togenerate one or more desired isotopes is described in more detail in theco-pending and commonly assigned application by the inventors entitled“Methods of Producing Isotopes in Power Nuclear Reactors”, Ser. No.11/002,680. Therefore, a detailed discussion of these processes isomitted herein for purposes of brevity.

FIG. 7 illustrates a rod assembly for a fuel bundle in accordance withanother exemplary embodiment of the invention. FIG. 7 illustrates a rodassembly 100′ in accordance with another exemplary embodiment of thepresent invention. In FIG. 7, only a few rod segments 110 of the rodassembly 100′ are shown for purposes of brevity, it being understoodthat the rod assembly 100′ could include additional rod segments 110 andspacers 20. In an example, the fuel bundle 10 may include eight spacers20 with various sized (different length) rod segments 110 attached tothe upper and lower end pieces 120 and 130 with an expansion spring 125attached atop the upper end piece 120, as is known in the art.

Unlike FIG. 2A, in FIG. 7 various sized adaptor ‘mini-subassemblies’ 300a may be provided at various locations such that connection pointsbetween two adjacent rod segments 110 do not occur at the spacerlocation (i.e., at spacer 20). FIG. 7 also illustrates an undercutsection 160 (segmented break line 360 in FIG. 2B) as well as a containerassembly 600′ in further detail. As it may be desirable to haveadditional locations to more easily remove rod segments 110 whichinclude a container assembly 600′ therein (for removal of the containerassembly 600′ and shipping to a desired customer), the rod assembly 100′may include different length adaptor subassemblies 300, such asmini-subassemblies 300 a and extended sub-assemblies to use betweenadjacent rod segments 110 of different lengths, for example. One or moreof the rod assemblies 100′ shown in FIG. 7 may be inserted into a fuelbundle such as the fuel bundle 10 shown in FIG. 1A. Additionally, a rodassembly 100 or 100′ could have both adaptor subassemblies 300 at spacer20 locations as well as one or more mini-subassemblies 300 a betweenspacers 20 for connecting adjacent rod segments 110, and/or forconnecting a rod segment 110 to one of an upper or lower end piece 120,130 (as shown in FIG. 2A) or one of an upper end piece assembly 1000 anda lower end piece assembly 1100 as shown in FIG. 7.

As also shown in FIG. 7, a given rod segment 110 may include multiplecontainer assemblies 600′ therein. In FIG. 7, the container assembly600′ may include a plurality of irradiation targets in “BB” form, whichis another alternative form for the irradiation target in accordancewith the present invention.

Accordingly, as shown in FIG. 7, the rod assembly 100′ may includevarious sized adaptor mini-subassemblies 300 a which may be used inaddition to the fixed-size adaptor subassembly 300 described in FIG. 2A.This may produce a single multi-joint rod assembly 100′ that has morethan one usage. This utilizes varying levels of neutron flux in thereactor for variations in the degree of isotope production in thetarget.

As an example, the rod assembly 100′ may contain a plurality ofirradiation targets at various locations within different sized rodsegments 110, and still maintain the same length of a standard fulllength fuel rod 18 or part length rod 19 within a fuel bundle 10 of FIG.1A, and/or provide a rod assembly 100′ having the same length as a partlength rod within fuel bundle 10 of FIG. 1A, for example. Different rodsegments 110 of the rod assembly 100′ may be removed and/or reconnectedat different connection points along the axially length of the rodassembly 100′. A given rod segment 110 and/or adaptor mini-subassembly300 a may be removed by unscrewing, cutting and/or snapping or breakinga specific section loose at its connecting point or at the undercutsection 160, for example.

Additionally as shown in FIG. 7, irradiation targets 620 may be placedin prepackaged container assemblies 600′ that may facilitate shippingdirectly from the reactor site to the receiving customer. Suchprepackaged containers 600′ may contain different irradiation targetmaterials, whether the target isotopes are in solid, liquid or gas formand placed inside a rod segment 110. For example, such is shown in FIG.13, which illustrates the multi-segmented fuel rod 100′ of FIG. 7 infurther detail. The multi-segmented fuel rod 100′ is broken up intovarious segments 110A, 110B, 110C, 110D, 110E, 110F and 110G thatconnect to each other via a corresponding adaptor subassembly 300 atconnection points 115 (as previously shown) to form a contiguousmulti-segmented fuel rod 100′ (as evident by the dotted connection lines111 in FIG. 13). FIG. 13 also illustrates enlargements ofcross-sectional views I-VII of the target container 600′ in each ofsegments 110A, 110C, 110E, 110F and 110G of the multi-segmented rod100′.

Enlarged views I and II show a plurality of containment structures 600′within rod 100′ that are housing multiple different targets, shown as aliquid, solid and a gas target 620 within a single rod segment 110A.Further, enlargements I and II illustrate indicia 650 that can be placedon the containment structures 600′ within a given rod segment 110A,110C, 110E, etc. As shown, the indicia 650 can indicate whether or notthe target is in solid, liquid or gas form, and can also provide thename of the target isotope and/or the name of the isotope to be produceddue to irradiation, for example (not shown in FIG. 13 for purposes ofclarity).

Rod segments 110B and 110D are shown to contain nuclear fuel 660, asshown in enlargements III and IV, for example. Of course in analternative, multi-segmented rod 100′ can be composed of a plurality ofrod segments 110 in which no segment 110 includes nuclear fuel, aspreviously described. Enlargement V of rod segment 110 e illustrates acontainer assembly 600′ which includes a target that is in gaseous form.Enlargement VI of rod segment 110F illustrates a container assembly 600′within the rod segment 110 f that includes a target 620 in liquid form.Enlargement VII of rod segment 110G illustrates a container assembly600′ which includes a solid target 620, shown as a single column ofCo-59BBs, which can be irradiated to produce the desire isotope, in thiscase, Co-60. Each of the container assemblies 600′ can thus beprepackaged with the target 620 isotope material in solid, liquid or gasform, for insertion into a corresponding rod segment 110 of themulti-segmented rod 100′, for example.

Further, since each of the container assemblies 600′ are sealed by endplugs 630 at one end 612 and by exterior threads 601 and an O-ring 602at the first end 611 (as previously shown in FIGS. 6A, 6D and 6E), theremoval of a particular segment 110 at its connection point 115 (i.e.,at the disconnection of the adapter subassembly 300 at connection point115 between two segments 110) will not cause a breach which would exposethe irradiation target 620 to the reactor coolant. Thus, the containerassembly 600′ together with the outer cladding of the rod segment 110provides a double-walled containment for the irradiation target 620.

FIGS. 8A-8B are views illustrating an adaptor subassembly for the rodassembly in accordance with another exemplary embodiment of theinvention; and FIGS. 9A-9B illustrate the mini-subassembly 300 a infurther detail. FIG. 8A shows a male adaptor plug 330′ and a directionof insertion into the female adaptor plug 350′. FIG. 8B illustrates theconnective engagement between male and female adaptor plugs 330′, 350′as part of an exemplary adaptor subassembly 300′.

FIGS. 8A and 8B illustrate a longer-length adaptor subassembly 300′ thanis shown in FIGS. 3A-3B and FIGS. 4A-4B, or in FIGS. 9A-9B. For example,the longer elongate section 338A of the longer male adaptor segment 330′may provide an adaptor subassembly 300′ which enables connection of asmaller length section of rod segment 110 to be interchangeable with amuch longer/heavier rod segment 110, should the need arise. In FIG. 8A,the length of the longer elongate section 338A is indicated as “y * n”so as to distinguish it from the length of the shorter elongate section338B in the mini-subassembly 300 a of FIG. 9A. Similarly, the overalllength of the adaptor subassembly 300′ in FIG. 8B may be longer than thecorresponding mini-subassembly 300 a in FIG. 9B by an integer multiplen, or by an addition of an integer n to the length ‘x’ ofmini-subassembly 300 a in FIG. 9B.

The smaller, two-piece mini-subassembly 300 a of FIGS. 9A-B may be usedin between spacer 20 locations for producing even smaller subassembliesof rod segments 110. The smaller two piece adaptor mini-subassembly 300a of FIG. 9B may be used in the same rod assembly 100′ as the larger twopiece adaptor subassembly 300′ shown in FIG. 8B, for example.

FIGS. 10A-B are views illustrating an upper end piece adaptor for therod assembly in accordance with another exemplary embodiment of thepresent invention. FIGS. 11A-B are views illustrating a lower end pieceadaptor for the rod assembly in accordance with another exemplaryembodiment of the present invention.

FIGS. 10A-11B illustrate alternative embodiments to the end pieceassembly 500 shown in FIGS. 5A and 5B. FIGS. 10A and 10B illustrate anupper end piece assembly 1000. The upper end piece assembly 1000 mayinclude an upper end piece adaptor subassembly 1330 at one end and theupper end piece 1310 connected thereto at another end, which may containthreads. Unlike the integral end piece assembly 500 shown in FIGS. 5Aand 5B, in FIGS. 10A and 10B, the upper end piece 1310 is attached to afemale adaptor plug 1350 similar to the female adaptor plug 350 asdescribed in FIGS. 4A and 4B. The female adaptor plug 1350 may beengaged to the male adaptor plug 1330 such as previously described abovein FIGS. 3A-3B. The upper end piece subassembly 1000 allows a fulllength rod from its upper end piece 1310 down to its bottom end piece2310 to be built by mixing and matching different lengths of rodsegments 110 to different connection points within the same axial lengthof the rod assembly 100′.

Similarly, in FIGS. 11A and 11B, a lower end piece assembly 1100 mayinclude a lower end piece adaptor subassembly 2300 connected to thelower end piece 2310. In particular, the lower end piece 2310 isattached to the male adaptor plug 2330, which mates with a femaleadaptor plug 2350 that is attached to an adjacent rod segment 110, forexample. In an aspect, the lower end piece may be used after the removalof a lower section of a rod segment 110, so that the remaining axiallength of the rod assembly 100′ can remain within the bundle 10 foradditional cycles using the detachable lower end piece assembly 1100.

Accordingly, the upper end piece assembly 1000 and lower end pieceassembly 1100 provide reusable and removable lower and upper end pieceswhich can facilitate quick repairs or removal of designated rod segments110 within the rod assembly 100′.

FIGS. 12A-C are views illustrating an adaptor subassembly for the rodassembly in accordance with another exemplary embodiment of theinvention. In general, adaptor subassembly 300 b may be understood as apush-snap locking mechanism having a male connector 330″ engaging acorresponding female connector 350″ to connect two rod segments 110 or arod segment 110 with one of the upper and lower end pieces 120/130 ofFIG. 2A. The male connector 330″ may include an expandable member at anend thereof, and the female connector 350″ may include an interiorcavity terminating in a receiver that is adapted to receive theexpandable member.

FIGS. 12A and 12B illustrates a male connector 330″ and female connector350″ and direction of connective engagement between the two connectors330″, 350″. As shown in FIG. 12B, the male connector 330″ may include aweld alignment member 355 (such as shown in FIG. 2B) to assist inaligning the male connector 330″ within the interior of itscorresponding rod segment 110. The other end of the male connector 330″may include a spring plug bayonet 1205 for connective engagement withinan interior cavity 358″ to terminate once fully engaged within acorresponding ball and socket joint fit-up 1210 of the female connector350″.

FIG. 12A illustrates a female connector 350″ with the interior cavity358″ that may be shaped so as to receive the spring plug bayonet 1205within the corresponding ball and socket joint fit-up 1210, as shown inFIG. 12A. FIG. 12C illustrates the connective engagement between thefemale 350″ and male 330″ connectors of connector subassembly 300 b.Accordingly, the rod segments 110 may be fully assembled into a singularrod assembly 100/100′ once the expandable bayonet plug spring collet1205 is fixedly secured within the ball and socket joint fit-up 1210 ofthe female connector 350″.

Accordingly, the adaptor subassembly 300 b in FIGS. 12A, 12B and 12Cillustrate a push-snap mechanism to connect adjacent rod segments 100 ofthe rod assembly 100/100′ and may reduce the sticking probability thatcould occur using the threaded engagement as shown in FIGS. 2A, 2B and7. This may lead to fast assembly and/or disassembly of various rodsegments 110, without the need for breaking, snapping, or cutting thesegments 110 apart, for example.

As previously described, each of the rod segments 110 may haveidentification marks or indicia thereon that identify the contents thatare within that particular rod segment 110. Alternatively, theidentification marks can be labeled on the container assemblies 600/600′within a given rod segment 110, for example.

In another aspect, the threaded screw length of the elongate sections338/338A/338B of FIGS. 8A-B and 9A-B on a given male adaptor plug 330may be of a sufficient length so that a given rod segment cannot becomeunscrewed during a reactor operation. As an example, the threaded screwlength of the elongate sections 338/338A/338B may be long enough suchthat it cannot come apart. This may help to ensure that a given rodlength would not become unscrewed during reactor operation.

In a further aspect, male adaptor plugs 330 and 330′, and/or maleconnector 330″ may be oriented in the same direction for ease ofextraction of a given rod segment 110. For example, segments 110 havingmale adaptor plugs 330, 330′ and/or 330″ may all be loaded and/orarranged in a given rod assembly 100/100′ so that the male adaptorplugs/connector 330, 330′, 330″ of the segment 110 extend verticallyupward toward the top of bundle 10, to facilitate grasping by a suitabletool for removal, installation, for example. In the event the rodsegment 110 is dropped, it would land with side having the femaleadaptor plug 350, 350′ and/or 350″ down, so as to reduce the chance thatthe male end snaps or breaks.

Accordingly, the exemplary rod assembly with multiple rod segmentsconnected thereto may provide a full length or part length rod. The rodassembly 100 may include adaptor subassemblies 300 which connectadjacent rod segments 110 at spacer 20 locations so as to eliminate theconsequences of fretting that is currently prevalent in full length andpart length rods of conventional fuel assemblies. In an aspect, the useof multiple rod segments 110 in a full length or part length rodassembly 100 or 100′ may allow for multiple irradiation targets to beloaded at different segments and at different axial locations of the rodassembly 100/100′. This may allow for multiple isotopes to be generatedin each fuel bundle of a reactor, should the reactor be configuredsolely for generating isotopes and/or for generating isotopes andproviding power generation, and also enables the ability to placeirradiation targets at desired flux locations along the axial length ofthe rod within a given fuel bundle.

The exemplary embodiments of the present invention being thus described,it will be obvious that the same may be varied in many ways. Suchvariations are not to be regarded as departure from the spirit and scopeof the exemplary embodiments of the present invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A fuel bundle for use in a nuclear reactor, the fuel bundlecomprising: a plurality of rods, at least one of the rods being amulti-segment rod, each multi-segment rod including, a plurality of rodsegments, the rod segments being removably mated to each other in anaxial direction, the rod segments being individually cladded, the rodsegments forming a continuous multi-segment rod having continuouscladding in the axial direction when so mated in the axial direction, atleast one rod segment being an adaptor subassembly containing noirradiation target, at least one irradiation target within a rodsegment; and a plurality of spacers, each spacer being spaced apart fromother spacers in the axial direction, each spacer directly contactingonly an adaptor subassembly along the axial length of the multi-segmentrods.
 2. The multi-segment fuel rod of claim 1, wherein the at least oneirradiation target does not include nuclear fuel.
 3. The multi-segmentfuel rod of claim 2, wherein another of the at least one irradiationtarget includes nuclear fuel.
 4. The multi-segment fuel rod of claim 1,wherein the at least one irradiation target is an isotope with an atomicnumber greater than
 3. 5. The multi-segment fuel rod of claim 1, whereinat least one rod segment contains a plurality of irradiation targets. 6.The multi-segment fuel rod of claim 1, wherein at least one rod segmentcontains at least one container assembly, the container assemblyincluding, a first end, a second end, at least one of the irradiationtargets, and an end cap configured to attach to at least one of thefirst and the second end to seal the irradiation target inside of thecontainer assembly.
 7. The multi-segment fuel rod of claim 6, whereinthe container assembly includes an exterior indicia indicating theirradiation target contained therein.
 8. The multi-segment fuel rod ofclaim 6, wherein the container assembly and the rod segment containingthe container assembly are sealed so as to provide double containmentfor the irradiation target.
 9. The multi-segment fuel rod of claim 1,wherein the rod segments are removably mated by at least one of anadaptor plug and receptor, a screw and threaded opening, and a tang andreceptor.
 10. The multi-segment rod of claim 1, wherein the irradiationtarget is Cobalt-59 that becomes Cobalt-60 when exposed to neutron flux.11. A method of fabricating a fuel bundle, the method comprising:forming a plurality of rods, at least one of the rods being amulti-segment rod, the forming the at least one multi-segment rodincluding, placing at least one irradiation target within at least oneof a plurality of rod segments, mating the plurality rod segments toeach other in an axial direction, the rod segments being individuallycladded, such that the rod segments form a continuous multi-segment rodhaving continuous cladding in the axial direction when mated, at leastone of the mated rod segments being an adaptor subassembly containing noirradiation target; and forming a fuel bundle including a plurality ofspacers and the plurality of rods by placing the plurality of rods intothe plurality of spacers such that each of the spacers directly contactsonly an adaptor subassembly along the axial length of the at least onemulti-segment rod.
 12. The method of claim 11, wherein the placing theat least one irradiation target includes, placing the at least oneirradiation target into at least one container assembly, the containerassembly including a first end, a second end, the at least oneirradiation target, sealing the at least one irradiation target insideof the container assembly with an end cap configured to attach to atleast one of the first and the second end, and placing the at least onecontainer assembly into the at least on of the plurality of rodsegments.
 13. The method of claim 12, further comprising: providing anexterior indicia on the container assembly, the exterior indiciaindicating the at least one irradiation target contained therein. 14.The method of claim 11, wherein the mating includes at least one ofmating an adaptor plug and receptor, mating a screw and threadedopening, and mating a tang and receptor.